Redefine the existence form and function of water in potassium carbonate-based deep eutectic electrolyte

Here, we prepared a green and novel deep eutectic electrolyte (DEE) consisting of potassium carbonate (PC) and ethylene glycol (EG). The formation mechanism and microstructure of deep eutectic solvent (DES) were studied by FTIR, 1H NMR and molecular dynamics simulation. And physicochemical properties of DES were further investigated by thermogravimetric analysis, differential thermal scanning analysis and conductivity measurement. The influence of H2O on the microstructure, physical properties and electrochemical properties of PC-EG electrolyte were systematically investigated. The results showed that PC-EG-20 where PC:EG molar ratio was 1:20 had a wide liquid range and the highest conductivity. The supercapacitor assembled from PC-EG-20 and activated carbon had a voltage window of 2.0 V, a specific capacitance of 190 F g−1 and an energy density of 23.89 Wh kg−1. Especially, the capacitor also exhibited a wide liquid range from −50 to 100 °C. Although the addition of H2O may reduce the electrochemical stability window of DEE, it can improve ionic conductivity and decrease viscosity, thereby improving capacitance and rate performance. This work may promote understanding and extend the application of DEE in supercapacitors.